Various processes and catalysts exist for the homopolymerization or copolymerization of olefins. For many applications, it is desirable for a polyolefin to have a high weight average molecular weight while having a relatively narrow molecular weight distribution. A high weight average molecular weight, when accompanied by a narrow molecular weight distribution, typically provides a polyolefin with high strength properties.
Traditional Ziegler-Natta catalysts systems comprise a transition metal compound co-catalyzed by an aluminum alkyl and are typically capable of producing polyolefins having a high molecular weight, but with a broad molecular weight distribution.
More recently metallocene catalyst systems have been developed wherein the transition metal compound has one or more cyclopentadienyl, indenyl or fluorenyl ring ligands (typically two). Metallocene catalyst systems, when activated with cocatalysts, such as alumoxane, are effective to polymerize monomers to polyolefins having not only a high weight average molecular weight but also a narrow molecular weight distribution.
Certain metallocenes containing substituted, bridged indenyl derivatives are noted for their ability to produce isotactic propylene polymers having high isotacticity and narrow molecular weight distribution. Considerable effort has been made towards obtaining metallocene-produced propylene polymers having ever-higher molecular weight and melting point, while maintaining suitable catalyst activity. Researchers currently theorize that there is a direct relationship between the way in which a metallocene is substituted, and the molecular structure of the resulting polymer. For the substituted, bridged indenyl type metallocenes, it is believed that the type and arrangement of substituents on the indenyl groups, as well as the type of bridge connecting the indenyl groups, determines such polymer attributes as molecular weight and melting point.
There is, therefore, significant interest in producing metallocene compounds with a variety of substituents on the arenyl ligands. However, current methods for producing substituted metallocene compounds, and especially Group 4 metallocene compounds, involve synthesis of each individual ligand family and then reaction with a simple metal derivative, such as MCl4 and M(N(CH3)2)4, where M=Ti, Zr, or Hf, using transmetallation and amine elimination reactions, respectively. This methodology requires preliminary ligand synthesis or modification, and, then, metallocene preparation starting from each ligand synthesized.
For example, U.S. Pat. No. 5,840,644 describes certain metallocenes containing aryl-substituted indenyl derivatives as ligands, which are said to provide propylene polymers having high isotacticity, narrow molecular weight distribution and very high molecular weight. However, synthesis of these compounds involves initial assembly of each aryl-substituted indene ligand from a substituted diphenyl compound and then reaction of the ligand with MCl4. Thus Example A discloses synthesis of rac-dimethylsilylbis(2-methyl-4-phenyl-indenyl)zirconium dichloride by reaction of 2-phenylbenzyl bromide with diethylmethyl malonate and then KOH to produce 2-(2-phenylbenzyl)propionic acid, followed by cyclization of the 2-(2-phenylbenzyl)propionic acid to produce 2-methyl-4-phenylindan-1-one and reduction of the 2-methyl-4-phenylindan-1-one to produce 2-methyl-7-phenylindene. The 2-methyl-7-phenylindene is then reacted with dimethyldichlorosilane to produce dimethylbis(2-methyl-4-phenylindenyl)silane, which is then reacted with butyllithium and zirconium tetrachloride to produce the desired bridged metallocene.
According to the present invention, a novel method of producing substituted metallocene complexes of early transition metals has been developed in which halogen substituents on existing metallocene compounds are directly replaced with other groups, such as hydrocarbyl groups. In this way, a single base synthesis of a given halogen-substituted metallocene compound can be used to generate a large number of final metallocene products with varying ligand substituents.
Modification of the coordinated ligands of late transition complexes, particularly, ferrocene derivatives, has been described (see Hassan, J.; Sevignon, M.; Gozzi, C.; Schulz, E.; Lemaire, M. Chem. Rev. 2002, 102, 1359, and references therein). However, no similar transformations of early transition metal complexes, which include highly polarized and reactive metal-ligand bonds, have been described so far.
Scarce examples of transformations of the coordinated cyclopentadienyl ligands of Group 4 metal complexes resulting in no modification of the nearest coordination polyhedron have been described, e.g. H/D exchange in η5-cyclopentadienyls (Larsonneur, A.-M.; Choukroun, R.; Jaud, J. Organometallics 1993, 12, 3216); Pd/C or PtO2 catalyzed hydrogenation of η5-indenyls giving η5-tetrahydroindenyls (Wild, F. R. W. P.; Zsolnai, L.; Huttner, G.; Brintzinger, H. H. J. Organomet. Chem. 1982, 232, 233. Schäfer, A.; Karl, E.; Zsolani, L.; Huttner, G.; Brintzinger, H. H. J. Organomet. Chem. 1987, 328, 87. Bandy, J. A.; Green, M. L. H.; Gardiner, I. M.; Prout, K. J. Chem. Soc., Dalton Trans. 1991, 2207. Rheingold, A. L.; Robinson, N. P.; Whelan, J.; Bosnich, B. Organometallics 1992, 11, 1869. Hollis, T. K.; Rheingold, A. L.; Robinson, N. P.; Whelan, J.; Bosnich, B. Organometallics 1992, 11, 2812); hydroboration of allyl- and vinyl-η5-cyclopentadienyl complexes (Erker, G.; Nolfe, R.; Aul, R.; Wilker, S.; Kriiger, C.; Noe, R. J. Am. Chem. Soc. 1991, 113, 7594. Erker, G.; Aul, R. Chem. Ber. 1991, 124, 1301); intramolecular photochemical [2+2] cycloaddition of vinyl-η5-cyclopentadienyl complexes (Erker, G.; Wilker, S.; Krüger, C.; Nolte, M. Organometallics 1993, 12, 2140); Ru-catalyzed metathesis of bis(allyl-η5-cyclopentadienyl)zirconium and -hafnium dichlorides (Ogasawara, M.; Nagano, T.; Hayashi, T. J. Am. Chem. Soc. 2002, 124, 9068).